This invention relates to a field emission device and a method for manufacturing the same.
When an electric field set to be about 10.sup.9 (V/m) is applied to a surface of a metal material or that of a semiconductor material, a tunnel effect occurs to permit electrons to pass through a barrier, resulting in the electrons being discharged to a vacuum even at a normal temperature. Such a phenomenon is referred to as "field emission" and a cathode constructed so as to emit electrons based on such a principle is referred to as "field emission cathode" (hereinafter also referred to as "FEC").
Recently, development of semiconductor fine-processing techniques permits a field emission cathode of the surface emission type to be constructed of field emission cathode elements having a size as small as microns. Arrangement of the thus-constructed field emission cathodes in large numbers on a substrate is expected to permit the field emission cathodes to act as an electron source for a display device of the flat type or any electronic device.
Such a field emission device may be manufactured according to, for example, a rotational oblique deposition method developed by Spindt, which is disclosed in U.S. Pat. No. 3,789,471.
Now, manufacturing of the field emission device by the Spindt method will be described with reference to FIGS. 10(a) to 10(c) and 11.
First, as shown in FIG. 10(a), a substrate 21 made of glass or the like is formed thereon with stripe-like cathodes 22, which are made of a metal layer by deposition and patterning. Then, a SiO.sub.2 layer 23 made by thermal oxidation of silicon and acting as an insulating layer is deposited on the substrate 21 so as to cover the cathodes 22, followed by formation of a gate layer on the insulating layer 23 by deposition or the like. The gate layer is made of a film of metal such as niobium (Nb) or the like.
Subsequently, a photoresist (not shown) is coated on the gate layer, followed by patterning of gates 24 in a manner to be substantially vertically perpendicular to the cathodes 22. Then, etching is carried out to form the gates 24 with apertures 25.
Then, the substrate 21 is subject to rotational deposition of aluminum (Al), which is carried out in a direction oblique to the substrate 21 while turning or rotating the substrate 21, leading to deposition of a peel layer. This results in the peel layer being selectively deposited on a surface of the gates 24 while being kept from being deposited in the apertures 25.
Thereafter, a molybdenum (Mo) layer is formed on the peel layer by deposition, so that emitters 27 of a conical shape (FIG. 11) may be depositedly formed in the apertures.
Succeedingly, the peel layer and deposited Mo layer on the gates 24 are removed therefrom by etching and then the gates 24 are formed thereon with a protective film layer 26, which is subject to patterning as shown in FIG. 10(c), to thereby provide protective films 26a for the gates 24. Subsequently, the gates 24 and cathodes 22 are subject to terminal lead-out processing, resulting in cathode terminals 22a and gate terminals 24a being formed.
Above the protective films 26a is arranged an anode substrate 29 in a manner to be spaced from the cathode substrate 21, as shown in FIG. 11. A seal 28 is interposedly arranged between both substrates 21 and 29, to thereby keep the space at a high vacuum when it is evacuated.
As shown in FIG. 11, the cathodes 22 are formed on the cathode substrate 21 and then a resistive layer is formed on each of the cathodes. The emitters 27 are arranged on the resistive layer. The gates 4 each are formed on the cathode 22 through the insulating layer 23 and the emitters 27 each are exposed at a distal end thereof through the aperture 25 of a circular shape.
In the thus-formed FEC of the surface discharge type, application of a drive voltage VGE of tens of volts between the gates 24 and the cathodes 22 permits the emitters 27 to emit electrons, which are then captured by the anode 29 which is spacedly arranged above the gate 24 and to which an anode voltage VA is applied.
When a phosphor is provided on the anode 29, it is excited by electrons captured by the anode 29, leading to luminescence.
As noted from the above, the FEC is so constructed that electrons travel in the space, thus, the cathode substrate 21 and anode substrate 29 are sealedly joined to each other through the seal 28, to thereby ensure operation of the FEC in a vacuum environment. Also, the seal 28 is arranged on the protective film 26a as shown in FIG. 10(c), to thereby prevent electrical disconnection in the FEC due to oxidation/reduction of the gate 24 by the seal 28, migration of the seal 28 or the like.
The protective film 26a, as shown in FIG. 10(b), is formed by subjecting the gate 24 to patterning on the insulating layer 23, forming the protective film layer 26 on the gate 24 by vapor deposition and subjecting the protective film layer 26 to patterning Thus, the prior art requires a step of independently preparing the protective film 26a.
Also, in the prior art, the cathode terminal 22a and gate terminal 24a are formed on the layers different from each other, respectively, as shown in FIG. 10(c), therefore, the terminal lead-out processing requires patternings carried out in steps different from each other.
Unfortunately, this causes manufacturing of the FEC to be highly complicated.